Project Summary Brucella spp. are bacteria that naturally infect a variety of domesticated and wild animals leading to abortions and sterility, and these bacteria are also capable of causing debilitating human infections, which often result from human exposure to infected animals and animal products. Brucella spp. are considered threats as potential biological weapons. Importantly, antibiotic treatment against brucellosis is prone to disease relapse, and there is currently no safe and effective vaccine to protect humans against infection with Brucella. The brucellae are intracellular pathogens that reside within immune cells called macrophages where they replicate in a specialized compartment, and the capacity of Brucella to survive and replicate within macrophages is essential to their ability to cause disease. Over the last few years, our laboratory has characterized a genetic pathway that is critical for the intracellular survival and pathogenesis of Brucella strains, and recently, we have discovered that one arm of this genetic circuitry controls the production of an ABC transport system, called GasABCDE, that is essential for Brucella virulence. Preliminary experiments revealed that GasE is required for the ability of Brucella abortus to colonize experimentally infected mice. Moreover, bioinformatic analyses determined that GasABCDE is homologous to ABC transporters in other closely related bacteria that function in the import of ?-aminobutyric acid (GABA), and experiments in our lab have demonstrated that GasABCDE is a bona fide GABA transporter in B. abortus. We have also demonstrated that GABA uptake by the brucellae results in transcriptional changes, leading to the hypothesis that Brucella strains use GABA as a means of sensing the intracellular environment of the host macrophage. Overall, very little is known about the role of GABA in bacterial pathogenesis, and the current project is designed to define how GABA and the transport of GABA are linked Brucella virulence. In the end, it may be possible to target bacterial GABA transport systems with novel vaccines and/or therapeutic strategies.